What Lake Bonneville Left Behind

At its peak, the ancient Lake Bonneville was an awe-inspiring sight, rivaling Lake Michigan in size and covering a vast expanse of western Utah, along with parts of Nevada and Idaho. As this massive Ice Age lake eventually receded, it shaped the landscape, leaving behind flat, shimmering playas and mineral-rich salt flats. These unique terrains would later become settings for remarkable feats of engineering, technological innovation, and dramatic tales of exploration and survival.

Lake Bonneville began to form approximately 55,000 years ago during a period of cooler, wetter climate. Volcanic activity in what is now southeastern Idaho altered the course of the Bear River, causing water to pool in Gem Valley and other nearby basins. For thousands of years, a natural dam at Red Rock Pass helped to contain the lake's waters.

Around 18,000 years ago, the accumulated water pressure caused the dam at Red Rock Pass to breach. This catastrophic event unleashed a colossal flood that flowed into the Columbia River system. In just six weeks, one of North America's most significant prehistoric floods caused lake levels to drop by over 350 feet (105 meters). As the climate subsequently warmed and dried, the lake drastically shrank, leaving behind the remnants we see today: the Great Salt Lake, Utah Lake, and Sevier Lake.

Though Lake Bonneville itself is long gone, its influence on the region's geology is still evident, even in satellite imagery. The Landsat 8 satellite, equipped with the Operational Land Imager (OLI), captured this image, revealing distinct bathtub-like rings and wave-cut terraces that mark the former shorelines. The dried lakebed, composed of fine-grained clay, marl, and sandy sediment deposited from the ancient waters, appears pale when contrasted with the darker, rockier, and more vegetated surrounding areas.

In the deeper sections of the basin, where runoff and groundwater continue to accumulate, bright deposits of evaporite minerals form extensive salt flats. These remarkably flat expanses are the result of gradual water evaporation, concentrating minerals like halite and gypsum, along with potassium- and magnesium-rich salts. These brines and deposits, particularly potash, a vital fertilizer ingredient, have long made the playa a valuable resource for mining, as indicated by the presence of rectangular evaporation ponds.

In contrast, the darker, more rugged terrain—including the Silver Island Mountains, the Newfoundland Mountains, and the Pilot Range—is composed of ancient bedrock layers, hundreds of millions of years old. These mountains also contain younger igneous and metamorphic rocks formed from magma intrusions into the ancient sedimentary sequences.

Crater Island, for example, is made up of sedimentary rocks, such as silica-rich sandstones and quartzites formed from sand accumulations in shallow seas. It also features intrusions of quartz monzonite, granites, and other igneous rocks. Later periods of crustal stretching resulted in the fault-block mountains that characterize the modern landscape.

Mapping these geological distinctions became a key focus in June 2026 when NASA scientists and engineers, involved with the DAVINCI mission to Venus, conducted field tests at Crater Island, often referred to as "Venus on Earth." They were testing the design of a camera system and instruments intended to descend through Venus's dense atmosphere and photograph its mountainous terrain with remarkable detail, surpassing the resolution of these Landsat images. The probe will capture near-infrared images, analyze atmospheric chemistry, and explore Venus's environment in unprecedented depth.

During the practice sessions at Crater Island, the camera system captured hundreds of images of various rock formations, including iron-rich and silica-rich units, while suspended from a helicopter as it descended. Using only these images, the team successfully created three-dimensional maps of the area that align with existing geological maps. This success provides confidence in their ability to map the geology of Alpha Regio, an analogous mountainous region on Venus that DAVINCI will study.

The flat, smooth expanses of Lake Bonneville's playas have also served as venues for achieving new land speed records. In 1960, Mickey Thompson made history as the first American to exceed 400 miles per hour, reaching 406.60 mph (654.36 km/h) in a streamlined car on the Bonneville Salt Flats. More recently, in August 2026, Andy Green set a record for the fastest land speed in a hydrogen-fueled internal-combustion vehicle, reaching 406.320 mph (653.909 km/h) without producing carbon dioxide.

Nearly two centuries earlier, in August 1846, members of the ill-fated Donner-Reed Party traversed the southern edge of Crater Island. Seeking a shortcut towards Pilot Peak, they journeyed from Hastings Pass, past Floating Island, and towards Donner Spring. However, their heavy wagons broke through the thin salt crust and became stuck in the mud beneath, a foreboding sign of the hardships to come. This delay led them to abandon several wagons in the desert.

NASA Earth Observatory images by Michala Garrison, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland.

References & Resources

• The Center for Land Use Interpretation, Intrepid Potash Wendover.
• Garvin, J.B., et al. (2022) Revealing the Mysteries of Venus: The DAVINCI Mission. The Planetary Science Journal, 3(117).
• Hill Air Force Base (2026, January 28) Traces of Travel: Donner-Reed Wagon Sites on the Hastings Cutoff.
• Idaho State University, Lake Bonneville Flood.
• NASA (2026, July 14) Utah Helicopter Flights Test NASA’s DAVINCI Mission to Venus.
• NASA, DAVINCI.
• NASA Earth Observatory (2018, February 25) Bonneville Salt Flats.
• National Park Service, Donner and Reed Wagon Train Incident.
• Utah Geological Survey, Lake Bonneville.
• Utah Geological Survey, Geologic History.
• Utah Geological Survey, Great Salt Lake and Lake Bonneville.
• Utah Department of Natural Resources (1990) Geologic Map of the Lucin 4 SW Quadrangle.